<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>数字圆</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        body {
            background-image: url(../img/beijing.jpg);
            background-size: cover;
            background-repeat: repeat;
        }

        .one {
            margin-left: 10px;
            margin-top: 10px;
            text-align: center;
            display: inline-block;
            width: 60px;
            height: 60px;
            line-height: 60px;
            border-radius: 50%;
            border: 2px red solid;
            color: white;
        }

        p {
            margin-block-start: 1em;
            margin-block-end: 1em;
            margin-inline-start: 0px;
            margin-inline-end: 0px;
        }

        .main {
            width: 650px;
            background-color: white;
            height: 300px;
            margin: auto;
            position: relative;
            top: 100px;
        }

        .main .one:nth-child(odd) {
            background-color: black;
        }

        .main .one:nth-child(even) {
            background-color: blue;
        }
    </style>
</head>

<body>
    <div class="main">
        <p class="one">
            <span>1</span>
        </p>
        <p class="one">
            <span>2</span>
        </p>
        <p class="one">
            <span>3</span>
        </p>
        <p class="one">
            <span>4</span>
        </p>
        <p class="one">
            <span>5</span>
        </p>
        <p class="one">
            <span>6</span>
        </p>
        <p class="one">
            <span>7</span>
        </p>
        <p class="one">
            <span>8</span>
        </p>
        <p class="one">
            <span>9</span>
        </p>
        <p class="one">
            <span>10</span>
        </p>
        <p class="one">
            <span>11</span>
        </p>
        <p class="one">
            <span>12</span>
        </p>
        <p class="one">
            <span>13</span>
        </p>
        <p class="one">
            <span>14</span>
        </p>
        <p class="one">
            <span>15</span>
        </p>
        <p class="one">
            <span>16</span>
        </p>
        <p class="one">
            <span>17</span>
        </p>
        <p class="one">
            <span>18</span>
        </p>
        <p class="one">
            <span>19</span>
        </p>
        <p class="one">
            <span>20</span>
        </p>
    </div>
</body>

</html>